The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor.
A Computer Program Listing Appendix is hereby expressly incorporated by reference. The Computer Program Listing Appendix includes two duplicate compact discs. The files on each compact disc, their size in bytes, and the date created are:
1. Technical Field
The present invention generally relates to an automated contact gage system using a three-axis contact contour comparator. More particularly, the invention relates to an automated contact gage system which employs a multiform contour scanner comparator which is capable of calibrating a wide range of dimensional forms/artifacts. The gage system can be employed for thread characterization (measurement), but is also capable of measuring high grade angle blocks, gage blocks, rolls, spherical forms, and virtually all manner of dimensional forms.
2. Related Art
Every fastening device owes its reliability and worth to its inherent dimensional properties. Dimensional properties can critically affect alignment properties which, in the case of certain machines or devices, can affect dynamic stability and even cause damage to or destroy the device or machine. Strength of the fastening device and the joinder accomplished by the device are important, but load distribution is also an important factor.
In the case of joinders by thread-type devices, the dimensions are embraced in the thread features which, in turn, are integral to the host cylinder. Load distribution, strength, functionality and reliability are all dependent on the dimensional properties. For example, too much load on a particular thread due to (for example) a deformed thread/cylinder can lead to shearing of that thread with obvious, detrimental consequences.
Threads are difficult to gage at the point where it counts (such as where a male device contacts a female device), so that wires have been used to make contact with both the right part of the thread and the gaging anvils. This is generally satisfactory, but it is costly and slow, making large samples impractical. Nevertheless, two or three points around the perimeter on the threads does not tell you much about the plug or the ring on which the threads are located. In addition, it tells you nothing about the load distribution properties of the device. For a comprehensive characterization of a fastener, one needs a robotized contour scanner that can gather and analyze large quantities of data in an unattended manner. With the infinitely fuller characterization afforded by a robotized scanner, one can begin to understand the fastener in question.
Although thread parameters are usually divided into major diameter, minor diameter, pitch diameter, lead, helical path, lead angle and taper, everything in between (which amounts to roundness and taper) is also important This is due to the fact that any deformation of the fastener can cause barrier thereof. Thus, the current generation of gages does not begin to meet the challenges associated with the development of modem fastening devices.
The following patents are considered to be representative of the prior art relative to the subject invention, but are burdened by various disadvantages discussed herein: U.S. Pat. No. 4,153,998 to McMurtry, entitled PROBES, issued on May 15, 1979, U.S. Pat. No. 5,822,877 to Dai, entitled MULTI-PROBE SYSTEM FOR DIMENSIONAL METROLOGY, issued on Oct. 20, 1998, U.S. Pat. No. 4,317,644 to Hosoi, entitled MACHINE TOOL PROFILING DEVICE, issued on Mar. 2, 1982, U.S. Pat. No. 4,785,545 to Aubele, entitled MEANS FOR SIMULTANEOUSLY CONNECTING A PLURALITY OF SWITCH-TYPE PROBE HEADS TO THE MEASUREMENT ARM OF A COORDINATE-MEASURING MACHINE, issued on Nov. 22, 1988, U.S. Pat. No. 5,917,181 to Yoshizumi et al., entitled PROFILE MEASURING APPARATUS, issued on Jun. 29, 1999, and U.S. Pat. No. 5,659,969 to Butler et al., entitled POSITION DETERMINING PROBE, issued on Aug. 26, 1997.
In particular, McMurtry, ""998 discloses a probe for determining at what point in space contact is made between an object and a stylus. It should be noted that, in FIG. 3 of the patent, dual bearings 9 and 10 along with an element 4 making up the probe 1 are disclosed. Similarly, Dai ""877 discloses a multi-probe system for dimensional metrology in which two ball bearings 516 and 518 and an element 502 which is spherically shaped and located adjacent to the bearings 516 and 518 are disclosed. The remaining patents disclose arrangements and features quite different from those disclosed and claimed herein. In short, none of these patents discloses an automated contact gage system employing a three-axis contact contour comparator, and capable of measurement in all three dimensions, as disclosed and claimed herein.
The present invention generally relates to an automated contact gage system using a three-axis contact contour comparator.
In general, the automated contact gage system of the present invention includes a left spindle and a right spindle connected by a spindle rail, the left spindle having a stylus arm mounted on a stylus arm vertical rail for contacting the workpiece to be gaged. The automated contact gage system also includes a control section for controlling movement of the various system elements in three different dimensions (X, Y and Z), the control system including a computer, printer and associated module, storage device, and X, Y and Z motor control units.
In further accordance with the invention, the movement of the stylus arm is controlled by a three-axis contact contour comparator arrangement including a bearing arrangement for contacting the stylus arm so as to guide and support it during contact with the workpiece or device being gaged. In a preferred embodiment, the bearing arrangement includes a spherical race and bearing, the spherical race preferably comprising five spherical elements or precision balls.
The automated contact gage system of the invention is unique in that it operates in accordance with three degrees of motion along X, Y and Z axes, respectively. Each axis has its own measurement sensor, which is, preferably, a fringe interferometer/scale line hybrid device. As will be apparent from the detailed description below, the system is completely automated, and no operator intervention is necessary once the device or workpiece to be gaged is mounted on the system for calibration.
Additionally, the hardware design of the automated contact gage system of the present invention is unique relative to arrangements of the prior art and other contemporary systems in that xe2x80x9chardxe2x80x9d real-environment engagement with the surface (either inner or outer) of the workpiece is achieved via a unique design of the stylus arm bearing arrangement.
In accordance with the invention, a single-element contact scanner collects virtually continuous, three-dimensional information relative to the surface of the workpiece. With the specimen mounted on the system, the stylus of the system guides the specimen into contact under selected pressure. The system of the invention is able to convert the derived three-dimensional information into test instrument (TI) dimensional characteristics with uncertainties below fifty micro-inches, and this capability results from the system""s capability of self-calibrating its own measurement elements using simple, smooth, well-characterized cylinder gages.
Finally, whereas prior and current conventional contact gages are virtually incapable of measuring certain parameters, such as root width and minor diameters (particularly with respect to wind-like structures), the present invention makes it possible to measure its own stylus thickness in real time under stress caused by the test instrument itself.
As a result of the aforementioned advantages, the present invention represents significant improvements over other past and current conventional gages, such as the following: go/no-go xe2x80x98feelxe2x80x99 output gages; parameter specific single point gages; optical comparators; lead machines; helical path analyzers; bench micrometers; scan/contact gages with contact contour scanners; and dental plaster.
The automatic contact gage system of the present invention employs a multiform contour scanner comparator capable of calibrating a wide range of dimensional forms/artifact. The gage system of the invention is capable of not only thread characterization on measurement, but also measurement of high grade angle blocks, gage blocks, rolls, spherical forms, and virtually all manner of dimensional forms.
In accordance with the invention, the surface to be gaged is contacted by an interchangeable, multi-purpose probe tailored for the application. The contact probe design optimizes xe2x80x9cholexe2x80x9d gaging or, on the other end of the spectrum, functions as a statistical or high point flat anvil. In either case, since the gage is preferably a comparator device, it does not require correction factors for individuals probes. This is in contrast to prior art arrangements wherein flat contact types of gages in at least one dimension are employed.
Inasmuch as the heart of any contact measurement system is its bearing, the present invention obtains high performance characteristics (+/xe2x88x9210 micro-inch) under ideal conditions as a result of the employment of a unique bearing arrangement comprising a precision spherical race and bearing combination. Preferably, the race comprises the intersection of three precision balls made to a preferable accuracy of +/xe2x88x925 micro-inch. Such a bearing arrangement is not present in the prior art.
In a preferred embodiment of the invention, the workpiece or device to be gaged is coupled to the system in one of two ways: free form (V-block or platinum); or centers or reverse centers. Furthermore, in the invention, there are three axes (X, Y, Z) of measurement motion known to +/xe2x88x9210 micro-inches. Each axis is sensed by its own respective sensor to +/xe2x88x9210 micro-inches, and communicates to the system control (preferably, a personal computer) through standard bus interfaces known to those of skill in the art. Each axis is driven by its own programmable step motor having a speed which is made to vary with friction and gravitational load imparted to the probe. Due to the construction of the stylus form employed in the invention, the probe must be xe2x80x9cpulledxe2x80x9d flanks and xe2x80x9cwalked downxe2x80x9d flanks. A unique orchestration of speed versus probe load allows the system of the invention to experience a resolution approaching the stated values in places of highest interest on the surface of the workpiece, and also speeds up the remainder of the characterization, thereby saving substantial operational time.
Finally, the gage is truly a three-dimensional gage since it never loses its original scan reference in the X, Y or Z axes. Therefore, separate scans can be united to obtain parameters, such as a helical path, previously obtainable only by separate, expensive and elaborate machines.
Therefore, it is an object of the present invention to provide an automated contact gage system using a three-axis contact contour comparator.
It is an additional object of the present invention to provide an automated contact gage system having a stylus arm which is guided and supported by a three-axis bearing arrangement.
It is an additional object of the present invention to provide an automated contact gage system comprising a left spindle, right spindle, stylus arm and three-axis bearing arrangement.
It is an additional object of the present invention to provide an automated contact gage system having a bearing arrangement which includes a spherical race and three spherical elements.
The above and other objects of the invention, and the nature of the invention, will be more clearly understood by reference to the following detailed description, the associated drawings, and the appended claims.